The present invention relates to aircraft avionics, and more particularly to aircraft radio altimeter test methods, apparatus and circuits.
Altimeters are a required instrument for most commercial or military aircraft. Altimeters function to allow the pilot to determine altitude (e.g., how far the aircraft is above the earth""s surface). Various types of altimeters exist, such as barometric altimeters (which rely on air pressure), radar altimeters (which rely on radio wave signals), frequency modulated (FM) altimeters and pulsed radio altimeters.
A typical radio altimeter works, for example, by transmitting or propagating a single radio frequency (RF) signal from the aircraft to the earth. The speed of the emitted radio frequency signal transmitted from the altimeter is a known value (e.g., the speed of light which is a known constant, or, approximately 299,792,458 meters per second). The emitted signal then reflects off the earth""s surface and returns to the aircraft at the same speed. The radio altimeter""s receiver receives the reflected signal, and, based upon the time the signal was transmitted from the aircraft to the time the signal was received by the radio altimeter, an altitude can be calculated. Radio altimeters, however, are not designed to operate at high altitudes. Radio altimeters do not typically operate at higher altitude because it is difficult to receive a signal reflected from the earth""s surface at the high altitudes aircraft fly. Thus, most radio altimeters are designed to operate closer to the vicinity of an earth surface, and more particularly, for example, at altitudes of 2,500 feet or less. As is known in the art, radio altimeters are an important flight instrument when the aircraft takes off as well as when the aircraft is in the process of landing.
The radio altimeter, however, may malfunction during operation. Because the radio altimeter only typically operates when the aircraft is close to the earth surface (e.g., at altitudes of 2,500 feet or less), there is no current method in which to test the operation of the radio altimeter while in flight at altitudes above 2,500 feet. Many of the radio altimeter""s components (e.g., such as transmission cables, antennas, processing means, the transmitter, the receiver and the like) could fail while in flight or even on the ground for various reasons. As such, it is necessary to calibrate the radio altimeter for proper operation.
It is therefore desirable to produce a test method and apparatus which tests the radio altimeter""s overall operational stability at any time, regardless of whether the aircraft is in flight or not, which results in a more accurate altimeter reading so that the aircraft achieve higher reliability and safety.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can only be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The present invention concerns a radio altimeter apparatus and method of testing a radio altimeter apparatus. In one embodiment, the present invention includes a radio altimeter having at least one signal processor in communication with a radio frequency (RF) transmitter, a transmit coupler in communication with the RF transmitter, a transmit switch in communication with the transmit coupler, a first load in communication with the transmit switch, a transmit antenna in communication with the transmit switch, a receive antenna, a receive switch in communication with the receive antenna, a second load in communication with the receive switch, a receive coupler in communication with the receive switch, a receiver in communication with both the receive coupler and the signal processor, and a variable attenuator in communication with the transmit coupler, the receive coupler and the signal processor.
In one embodiment, the present test method encompasses transmitting a RF signal internally through the altimeter at full power and evaluating the performance of the altimeter, which may be useful in aircraft auto land (e.g., aircraft landing automatically by instrument) procedures.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.